Question

what is the explaination given for not losing energy of electrons while revolving around the nucleus

Answer 1

According to Bohr's model of the atom:
An atom consists of a small heavy positively charged nucleus in the centre surrounded by electrons. The electrons in an atom revolve around the nucleus only in certain selected circular paths called orbits. As long as the electrons remains in a particular orbit, it does not lose or gain energy. This means that the energy of the electron in a particular energy shell remains constant. Therefore, these orbits are also called stationary states. The term stationary does not mean that electron is stationary but it means that the energy of the electron does not change with time. This accounts for the stability of an atom.